Waste heat capture from a dual fuel gas and electric water heater

ABSTRACT

A dual fuel—gas fuel and electric heat pump—water heater is provided that captures waste heat from the exhaust flue of the gas fuel heating system and utilizes it in the evaporator of the electric heat pump. Multiple mechanisms are disclosed for the transfer of heat from the exhaust flue gases to the evaporator. Heat from the exhaust gas that would otherwise be lost is used to help heat refrigerant in the evaporator to improve the efficiency of the system. This heat can also be used to prevent or remove frozen condensate on the evaporator.

FIELD OF THE INVENTION

The subject matter of the present disclosure relates generally to a dual fuel water heater designed to transfer waste heat from an exhaust flue of a gas fuel heating system to an evaporator of an electric heat pump.

BACKGROUND OF THE INVENTION

Water heaters can provide for the heating and storage of water to be used in, e.g., a residential or commercial structure. While water heaters can be provided in a variety of shapes and sizes, a typical shape includes an elongated cylindrical tank. In some water heaters, the tank may be configured for a vertically upright position and be surrounded by insulation and an exterior wrapper or jacket. A heat source is provided for raising the temperature of water in the tank. The heat energy may be supplied by, e.g., gas burners, electrically-resistant coils, an electric heat pump using a refrigerant cycle, or a combination thereof.

In one construction, a water heater may utilize both gas fuel burners and an electric heat pump using a refrigerant cycle to heat the water in the tank. The gas fuel heating system may place gas burners underneath the tank and provide thermal energy to the tank through combustion of the gas fuel. Additionally, the electric heat pump may wrap a plurality of coils around the cylindrically-shaped exterior wall of the water tank. In this configuration, the coils serve as a heat exchanger, also referred to as a condenser, through which hot refrigerant flows around the tank. This configuration enables heat transfer from the hot refrigerant, through the coils and the tank walls, and then to the water.

Certain challenges exist with this construction, however. Such construction, for example, can have inefficiencies as significant heat loss can occur from the gas fuel heating system in form of exhaust gas exiting through the exhaust flue. Additionally, when a water heater of this construction is operated in conditions that are near or below freezing, the condensation on the evaporator of the heat pump may freeze, impeding air flow over the evaporator. As a result, some water heaters of this construction require a reversing flow valve for the heat pump, a defrost heater, or other similar device to melt the frozen condensate on the evaporator. However, utilizing these or similar devices may lead to an inefficient water heater system and adds complexity to the manufacture and operation of the water heater.

Accordingly, a dual fuel—gas fuel and electric heat pump—water heater having one or more features that can improve the efficiency of the water heater would be useful. More particularly, such a water heater that can capture and utilize the waste heat from the exhaust flue of the gas fuel heating system would be beneficial. Such a water heater that could also remedy frozen condensate on the evaporator would also be useful.

BRIEF DESCRIPTION OF THE INVENTION

The present disclosure provides a dual fuel—gas fuel and electric heat Pump—water heater that captures waste heat from the exhaust flue of the gas fuel heating system and utilizes it in the evaporator of the electric heat pump. Multiple mechanisms are disclosed for the transfer of heat from the exhaust flue gases to the evaporator. Heat from the exhaust gas that would otherwise be lost is used to help heat refrigerant in the evaporator to improve the efficiency of the system. This heat can also be used to prevent or remove frozen condensate on the evaporator. Multiple features as described herein may be used to further improve heat transfer as well. Additional aspects and advantages of the invention will be set forth in part in the following description, or may be apparent from the description, or may be learned through practice of the invention.

In one exemplary embodiment, the present disclosure provides a water heater that includes a tank for holding water. It may also include a gas fuel heating system configured for heating the water in the tank. The gas fuel heating system may include an exhaust flue, wherein the exhaust flue has an exterior surface. The water heater may also include a heat pump heating system, which may also be configured for heating the water in the tank. The heat pump heating system may include an evaporator. Additionally, the water heater may include a pipe. The pipe may be in thermal communication with the exhaust flue and the evaporator and configured for transferring heat from the exhaust flue to the evaporator. The water heater may also include a fan configured for causing the flow of air past the exhaust flue and over the evaporator.

In another exemplary embodiment, the present disclosure provides a water heater that includes a tank for holding water. It may also include a gas fuel heating system configured for heating the water in the tank. The gas fuel heating system may include an exhaust flue. The water heater may also include a heat pump heating system, which may also be configured for heating the water in the tank. The heat pump heating system may include an evaporator. Additionally, the water tank may include a fan configured for causing an air flow over the evaporator and past the flue so as to provide for heat transfer from the flue to the evaporator.

In yet another exemplary embodiment, the present disclosure provides a water heater that includes a tank for holding water. It may also include a gas fuel heating system configured for heating the water in the tank. The gas fuel heating system may include an exhaust flue that facilitates the flow of exhaust, wherein the exhaust includes heated gases from the gas fuel heating system. The water heater may also include a heat pump heating system, which may also be configured for heating the water in the tank. The heat pump heating system may include an evaporator. Additionally, a portion of the exhaust from the exhaust flue may flow over the evaporator.

These and other features, aspects, and advantages of the present disclosure will become better understood with reference to the following description and appended claims. The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the disclosure and, together with the description, serve to explain the principles of the disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

A full and enabling disclosure of the present disclosure, including the best mode thereof, directed to one of ordinary skill in the art, is set forth in the specification, which makes reference to the appended figures, in which:

FIG. 1 is a cross-sectional side view of an exemplary embodiment of a water heater of the present disclosure.

FIGS. 2 and 3 are close-up side views of two exemplary embodiments of an exhaust flue and an evaporator of a water heater of the present disclosure.

FIG. 4 is a close-up, cross-sectional top view of an exemplary embodiment of an exhaust flue of a water heater of the present disclosure.

FIG. 5 is a close-up side view of an exemplary embodiment of an exhaust flue of a water heater of the present disclosure.

FIGS. 6 and 7 are close-up side views of exemplary embodiments of an evaporator of a water heater of the present disclosure.

FIGS. 8, 9, and 10 are close-up side views of three exemplary embodiments of an exhaust flue and an evaporator of a water heater of the present disclosure.

DETAILED DESCRIPTION OF THE INVENTION

Reference now will be made in detail to embodiments of the invention, one or more examples of which are illustrated in the drawings. Each example is provided by way of explanation of the invention, not limitation of the invention. In fact, it will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the scope or spirit of the invention. For instance, features illustrated or described as part of one embodiment can be used with another embodiment to yield a still further embodiment. Thus, it is intended that the present invention covers such modifications and variations as come within the scope of the appended claims and their equivalents.

FIG. 1 provides a cross-sectional side view of an exemplary embodiment of a vertically oriented water heater 100 of the present disclosure. In this embodiment, water heater 100 includes a tank 124 for storing water. Tank 124 defines a radial direction R and a vertical direction V. In FIG. 1, vertical direction V runs parallel to the axial direction of tank 124. Notably, however, in other exemplary embodiments, tank 124 may be horizontally oriented, in which case radial direction R of tank 124 would be approximately parallel with the vertical direction, and the axial direction of tank 124 would be approximately parallel with the horizontal direction.

Tank 124 may be positioned within an outer jacket 98 that surrounds tank 124 to create an annular space 146 between tank 124 and jacket 98. Insulation 126 may be provided within annular space 146 to reduce the amount of heat transfer from tank 124 to the environment. Insulation 126 may be provided as foamed-in insulation, but other materials may be used as well.

Tank 124 extends between a pair of end portions or, more particularly, between a bottom portion 170 and a top portion 172. Top portion 172 may include a water outlet 122 with associated coupling 114 and a water inlet 120 with associated coupling 116. Coupling 114 may connect with conduit 110, and coupling 116 may connect with conduit 112, and each may extend through housing 102. In turn, conduits 110 and 112 can each be fitted with couplings 106 and 108, respectively, for connection of water heater 100 to the piping or plumbing associated with a water supply system of, e.g., a commercial or residential structure. Coupling 108 may be connected with, e.g., a pipe delivering a pressurized water supply that flows into tank 124 using dip tube 118. In turn, heated water may be returned to such piping system through the connection provided by coupling 106.

In an alternative embodiment of the present disclosure, however, water outlet 122 may include conduit 110 welded to tank 124 and water inlet 120 may include conduit 112 welded to tank 124, each having no separate couplings for connection to tank 124. Additionally, instead of couplings 106 and 108, conduits 110 and 112 may include a threaded portion and pipe nipples for connection of water heater 100 to the piping or plumbing associated with a water supply system of, e.g., a commercial or residential structure.

Bottom portion 170 of tank 124 may include a circular bottom edge 142 and a bottom wall 128. Beneath bottom wall 128 is a gas fuel heating system 224, which may include a combustion chamber 208. Within combustion chamber 208 may be one or more gas burners 206. Gas burner 206 may be constructed of a circular plate with a series of burner holes 222 positioned along an edge of the circular plate. Gas fuel and air may enter the burner through a burner inlet 220 positioned at a side of the gas plate or, alternatively, burner inlet may be positioned underneath the circular plate. Gas burners 206 heat the water in tank 124 by providing thermal energy to tank 124 through combustion of a gas fuel. A separate pilot light may be provided to ignite the gas fuel and air as it exits burner holes 222, such that flames are provided that come up and around the circular plate. The gas fuel may be supplied by, e.g., a gas line from consumer's house supply 214, which in turn may be connected to a gas control mechanism 216, configured for providing the gas fuel to burners 206 through gas line 218. Other constructions and configurations of gas fuel heating system 224, as are well known in the art, are contemplated by the present disclosure as well.

The exhaust air from the combustion of gas fuel in combustion chamber 208 exits through an exhaust flue 174. Exhaust flue 174 may extend through the center of tank 124 and out through housing 102, where it may then connect with a vent to, e.g., the consumer's chimney 204 using a draft hood 202. Exhaust flue 174 may have a diameter that is approximately twice the size shown in FIG. 1, such as from between 3 inches and 5 inches. Additionally, exhaust flue 174 may include one or more restrictive baffles (not shown) to slow down and create turbulence in the exhaust gas. This may allow for increased heat transfer from exhaust flue 174 to the water in tank 124.

Mounted to top 172 is housing 102, which houses an electric heat pump heating system 104 using a refrigerant cycle. Heat pump heating system 104 may be used to heat the water in tank 124 in conjunction with or in alternative to gas fuel heating system 224. Heat pump heating system 104 employs coils 130 to circulate hot refrigerant around tank 124 and heat water in tank 124. Coils 130 operate as a heat exchanger or, more particularly, as a condenser for heat pump heating system 104. As will be understood by one of skill in the art, compressed refrigerant vapor flowing through coils 130 condenses to a liquid in coils 130 to provide heat to water in tank 124. The refrigerant in coils 130 then flows through an expansion valve, wherein the refrigerant is depressurized and the temperature of the refrigerant drops. The refrigerant then flows through an evaporator 178, wherein air may be moved past evaporator 178 to begin warming the refrigerant prior to the refrigerant being compressed and sent back around tank 124. A fan 226, configured for creating a flow of air over evaporator 178 in an air flow direction F, may be provided. Water heater 100 is provided by way of example only. Using the teachings disclosed herein it will be understood that other configurations, constructions, or shapes for water heater 100 with heat pump heating system 104 and gas fuel heating system 224 may be used as well.

The configuration of water heater 100 is provided by way of example only. As will be understood by one of skill in the art using the teachings disclosed herein, the present invention includes water heaters of other constructions and configurations as well.

For reasons previously stated, it is desirable to capture the waste heat from exhaust flue 174 of gas fuel heating system 224 and utilize it in evaporator 178 of heat pump heating system 104. Such a configuration will provide a heat pump heating system having increased efficiency, as well as providing increased efficiency in water heater 100 as a whole. Additionally, the waste heat from exhaust flue 174 may be utilized to defrost evaporator 178, or prevent evaporator 178 from accumulating frost.

FIG. 2 provides an exemplary embodiment of the present disclosure, wherein water heater 100 includes a heat pipe 176 to transfer waste heat from exhaust flue 174 of gas fuel heating system 224 to evaporator 178 of heat pump heating system 104. A fan 226 is configured for creating a flow of air past exhaust flue 174 and over evaporator 178. In one exemplary embodiment, as shown in FIG. 2, pipe 176 may capture waste heat from exhaust flue 174 by extending in the vertical direction along exterior surface 196 of exhaust flue 174. Further, pipe 176 may transfer the waste heat captured from exhaust flue 174 by also extending in the vertical direction adjacent to evaporator 178, and by being positioned upstream from evaporator 178 in the air flow direction F created by fan 226. A variety of configurations may be used for providing heat transfer between pipe 176, exhaust flue 174, and evaporator 178.

In one exemplary embodiment, pipe 176 may be comprised of a solid material for transferring heat by conduction, whereas in another exemplary embodiment pipe 176 may carry a heat transfer fluid for transferring heat using the sensible and/or latent heat of the fluid. As used herein with regard to pipe 176, the term “pipe” is not limited to a circular shape in cross-section or to a tube and refers, instead, to a medium for conducting heat as described herein.

In one exemplary embodiment the transfer fluid may be a single phase fluid. As used herein, a “single phase fluid” is a material that does not change phases as it passes through pipe 176 and is heated and cooled by exhaust flue 174 and evaporator 178.

When a single phase fluid is used, pipe 176 may be positioned along exhaust flue 174 and evaporator 178 so as to allow the fluid to act as a thermosyphon, where natural convection will move fluids in pipe 176 from exhaust flue 174 to evaporator 178. More particularly, as shown in the exemplary embodiment of FIG. 2, pipe 176 may extend vertically upward along axial direction A of exhaust flue 174. This allows fluid to move upward along vertical direction V in pipe 176 as it is heated while travelling next to exhaust flue 174. Pipe 176 may also extend vertically downward along evaporator 178 so that as fluid in pipe 176 cools and becomes more dense, it can move vertically downward along evaporator 178 and return to exhaust flue 174. For the exemplary embodiment shown, a leg 177 of heat pipe 176 extending between the exhaust flue 174 and evaporator 178 is angled upwardly therebetween so as to allow heated fluid to in pipe 176 to move towards evaporator 178. Other configurations may be used as well.

In yet another exemplary embodiment, pipe 176 may carry a phase change fluid. As used herein, a phase change fluid refers to a material that is capable of storing a relatively large amount of energy when it changes phase between, e.g., a gas and liquid or between a liquid and a solid. By way of example, for pipe 176 of the present disclosure, phase change fluids that may be used include dichlorodifluromethane, trichlorofluromethane, benzene, methanol, ammonia, water, mercury, and mixtures thereof. Other materials may be used as well. By way of example, where a phase change material is used, the configuration of pipe 176 can be similar to that shown in FIGS. 2. However, as is discussed below, other configurations of pipe 176 are contemplated as well.

Referring now to FIG. 3, in one exemplary embodiment, pipe 176 may capture waste heat from the exhaust flue by wrapping around exterior surface 196 of exhaust flue 174 one or more times. Pipe 176 may then transfer the waste heat captured from exhaust flue 174 to evaporator 178 by extending adjacent to evaporator 178, and by being positioned upstream from evaporator 178 in the air flow direction F created by fan 226. Additionally, pipe 176 may extend across evaporator 178 one or more times. In another exemplary embodiment, as shown in FIG. 3, evaporator 178 may contain a plurality of grooves 190, and pipe 176 may further be positioned within grooves 190. This configuration may assist in holding pipe 176 in position and may increase the amount of heat transfer between pipe 176 and evaporator 178. With each of the above exemplary embodiments, however, pipe 176 may be comprised of a solid material, a single phase fluid, or a phase change fluid, as previously discussed.

In another exemplary embodiment, as shown in FIGS. 4 and 5, a portion of pipe 176 may extend around a portion of exhaust flue 174 to form a partial sleeve 192 around exhaust flue 174. In this exemplary embodiment, exhaust flue 174 further defines a radial direction, R. As shown in the cross-sectional top view of FIG. 4, partial sleeve 192 may have an interior surface 194 that has a semi-circular shape as viewed in a plane containing radial direction R, which shape approximately matches the shape of exterior surface 196 of exhaust flue 174 in radial direction R. Further, as shown in the side view of FIG. 5, partial sleeve 192 may extend along exterior surface 196 of exhaust flue 174 in axial direction A for a defined length.

Pipe 176 may be affixed to evaporator 178 in a number of ways. In one exemplary embodiment, pipe 176 may be welded to evaporator 178. As previously discussed, in an alternative exemplary embodiment, pipe 176 may be fitted integrally to evaporator 178 by positioning pipe 176 within grooves 190 defined by evaporator 178. This embodiment is illustrated in FIG. 3. In yet another exemplary embodiment, pipe 176 may be attached to evaporator 178 by a plurality of hooks 188, as is shown in FIG. 6. In this exemplary embodiment, hooks 188 may be attached to pipe 176 and then hooked into evaporator 178 or vice versa. Hooks 188 may be comprised of a metal, which may assist in heat transfer by acting as a heat exchanger between pipe 176 and evaporator 178.

Referring now to FIG. 7, in one exemplary embodiment of the present disclosure, pipe 176 may run adjacent to evaporator 178, without physically touching it. Additionally, pipe 176 may be positioned upstream from evaporator 178 in the air flow direction F created by fan 226. Further, as is shown in FIG. 7, a portion of pipe 176 may comprise a plurality of fins 186. Fins 186 may assist in transferring waste heat captured by pipe 176 to the air flow and then to evaporator 178. The portion of pipe 176 with fins 186 may extend across the air flow path to evaporator 178 one or more times.

Referring now to FIG. 8, in still another exemplary embodiment of the present disclosure, water heater 100 may transfer waste heat from exhaust flue 174 to evaporator 178 by having exhaust flue 174 define a plurality of branches 200 along axial direction A, wherein each branch is configured for carrying exhaust air. The branches 200 may also be configured for allowing air to pass between branches 200 and over evaporator 178, and may be positioned upstream from evaporator 178 in the air flow direction F created by fan 226. The addition of branches 200 to exhaust flue 174 exposes additional surface area of exhaust flue 174 to the air passing by exhaust flue 174 and over evaporator 178. This may allow for an increased transfer of waste heat from exhaust flue 174 to evaporator 178. Branches 200 may rejoin to form a single exhaust flue 174, as shown in FIG. 8.

In yet another exemplary embodiment of the present disclosure, shown in FIG. 9, water heater 100 may transfer exhaust heat from exhaust flue 174 to evaporator 178 by having exhaust flue 174 includes a plurality of fins 184. In this exemplary embodiment, fan 226 is configured for causing a flow of air past fins 184 and over evaporator 178, wherein exhaust flue 174 is positioned upstream from evaporator 178 in the air flow direction F created by fan 226. This configuration may assist in the transfer of waste heat from exhaust flue 174 to evaporator 178.

In still another exemplary embodiment of the present disclosure, waste heat from exhaust flue 174 may be transferred to evaporator 178 by diverting a portion of the exhaust air, including heated gases from gas fuel heating system 224, from exhaust flue 174 over evaporator 178, as is shown in FIG. 10. In one exemplary embodiment, the amount of exhaust air that flows over evaporator 178 may be fixed. For example, a small portion of the exhaust air may be diverted to flow over evaporator 178, or all of the exhaust air may be diverted to flow over evaporator 178, or anywhere in between. In another exemplary embodiment, the amount of exhaust air that flows over evaporator 178 may be varied depending on the operating conditions of water heater 100. For example, the entire stream of exhaust air from exhaust flue 174 may be diverted over evaporator 178 when gas fuel heating system 224 is not being operated, while only a portion of the exhaust air from exhaust flue 174 may be diverted over evaporator 178 when gas fuel heating system 224 is being operated.

This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they include structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims. 

What is claimed is:
 1. A water heater, comprising: a tank for holding water; a gas fuel heating system configured for heating the water in said tank, said gas fuel heating system comprising an exhaust flue, said exhaust flue defining an exterior surface; a heat pump heating system configured for heating the water in said tank, said heat pump heating system comprising an evaporator; a pipe in thermal communication with said exhaust flue and said evaporator, wherein said pipe is configured for transferring heat from said exhaust flue to said evaporator; and a fan configured for causing a flow of air past said exhaust flue and over said evaporator.
 2. A water heater as in claim 1, wherein said pipe is comprised of a solid material for conducting heat between said exhaust flue and said evaporator.
 3. A water heater as in claim 1, further comprising a single phase transfer fluid transported within said pipe for conducting heat between said exhaust flue and said evaporator.
 4. A water heater as in claim 1, further comprising a phase change fluid contained within said pipe for conducting heat between said exhaust flue and said evaporator.
 5. A water heater as in claim 4, wherein said phase change fluid is selected from the group consisting of dichlorodifluromethane, trichlorofluromethane, benzene, methanol, ammonia, water, mercury, and mixtures thereof
 6. A water heater as in claim 1, wherein said pipe wraps around the exterior surface of said exhaust flue one or more times.
 7. A water heater as in claim 1, wherein said flue defines an axial direction, and wherein said pipe extends adjacent to said flue and in contact with said flue along the axial direction.
 8. A water heater as in claim 1, wherein a portion of said pipe extends around a portion of said exhaust flue and forms a partial sleeve around said exhaust flue.
 9. A water heater as in claim 1, wherein a portion of said pipe runs adjacent to said evaporator.
 10. A water heater as in claim 9, wherein a portion of said pipe extends across the path of air flow to said evaporator at least one time.
 11. A water heater as in claim 9, wherein said evaporator defines a plurality of grooves, and wherein said pipe is positioned within the plurality of grooves defined by said evaporator.
 12. A water heater as in claim 9, wherein said pipe is attached to said evaporator using a plurality of hooks.
 13. A water heater as in claim 9, wherein said pipe is welded to said evaporator.
 14. A water heater as in claim 1, wherein a portion of said pipe is located adjacent to said evaporator in a path of air flow over the evaporator, and wherein a portion of said pipe comprises a plurality of fins.
 15. A water heater as in claim 14, wherein a portion of said pipe extends across the path of air flow to said evaporator at least one time.
 16. A water heater, comprising: a tank for holding water; a gas fuel heating system configured for heating the water in said tank, said gas fuel heating system comprising an exhaust flue; a heat pump heating system configured for heating the water in said tank, said heat pump heating system comprising an evaporator; and a fan configured for causing an air flow over said evaporator and past said flue so as to provide for heat transfer from said exhaust flue to said evaporator.
 17. A water heater as in claim 16, wherein said exhaust flue defines an axial direction, and wherein said exhaust flue defines a plurality of branches extending along the axial direction with each branch configured for carrying exhaust gases, wherein the branches are positioned so as to allow the air flow from said fan to pass between the branches.
 18. A water heater as in claim 16, wherein a portion of said exhaust flue defines a plurality of fins.
 19. A water heater, comprising: a tank for holding water; a gas fuel heating system configured for heating the water in said tank, said gas fuel heating system comprising an exhaust flue that facilitates the flow of exhaust comprising heated gases from the gas fuel heating system; a heat pump heating system configured for heating the water in said tank, said heat pump heating system comprising an evaporator, wherein a portion of the exhaust from said exhaust flue flows over said evaporator.
 20. A water heater as in claim 19, wherein the amount of exhaust that flows through the evaporator is varied depending on operating conditions of the water heater. 